Heat treatable coated glass

ABSTRACT

A heat-treatable coated glass article comprises a substantially transparent substrate with a substantially transparent dual-function coating on a surface of the substrate. The coating provides low emissivity and high anti-solar performance properties. It comprises a first anti-reflection layer of dielectric material, preferably tungsten oxide. An infra-red reflective layer of silver metal and/or copper metal overlies the anti-reflection dielectric layer. A buffer layer, such as a chromium buffer layer, is positioned between the anti-reflection layer and the infra-red reflective layer. Also, optionally, a color control layer may be used, preferably being positioned between the anti-reflection layer and the substrate. A second buffer layer directly overlies the infra-red reflective layer. A second anti-reflection layer overlies the second buffer layer. In accordance with a method of manufacturing the coated article, each of the layers of the coating is deposited in turn by D.C. magnetron sputtering in a multi-station sputtering chamber. Passing the transparent substrate through the sputtering chamber a second time to produce a double-layer coating structure is found to provide especially high quality performance characteristics.

INTRODUCTION

The present invention is directed to transparent substrates havingmulti-layer coatings for thermal insulation properties, as well as tomethods of manufacturing such multi-layer coated articles. The inventionrelates, in particular, to coated, transparent glass substrates whichare heat treatable. Certain preferred embodiments are suitableespecially for automotive and architectural applications, exhibitinghigh visible light transmittance and high infra-red (IR) energyreflectance.

BACKGROUND

Coated glazing products having anti-solar properties, that is, lowtransmittance of to wavelengths in the infra-red range, are known tothose skilled in the art. Coatings for glazing products are disclosed,for example, in European patent application 0 646 551 A1 entitledHeat-Treatment Convertible Coated Glass and Method of Converting Same.That document discloses silver coatings comprising a layer Of Si₃N₄ overa layer of nickel or nichrome, over a layer of silver, over a secondlayer of nickel or nichrome, over a second layer Of Si₃N₄. Sputtering isdisclosed for producing such coating. Sputtered deposition of amulti-layer coating is described, for example, in European PatentApplication 0,418,435 to Nalepka. The multi-layer coating of Hayward etal. is said to comprise a layer of sputtered zinc, tin, titanium,indium/tin or bismuth oxide, next a layer of sputtered silver or silveralloy, then a layer sputtered titanium or stainless steel and finally alayer of zinc, tin, titanium, indium/tin or bismuth oxide. Suchmulti-layer film is said to have excellent visible light transmissionwhile controlling both near infra-red solar energy and far infra-redreflected energy. A temperable coated article is suggested in U.S. Pat.No. 5,552,180 to Finley et al. The coated article of Finley et al.employs a metal-containing film such as titanium nitride whichordinarily oxidizes at the high temperatures encountered during glasstempering, along with an overcoating of a protective layer of a siliconcompound and an undercoating with a stabilizing metal-containing layer.In U.S. Pat. No. 3,990,784 to Gelber a multi-layer coating forarchitectural glass is suggested, comprising first and second metallayers with a dielectric layer disposed between them. Gelber suggeststhat the transmission properties of the coating can be changedindependent of its reflection properties, by varying the thickness ofthe metal layers while maintaining the ratio of their thicknessesconstant.

Similar coatings are disclosed in European Patent Application 97104710.5published as EP0796 825 A2, wherein a low emissivity sputtered coatingemploys controlled index of refraction of an undercoat layer of anappropriate dielectric material below a first Si₃N₄ layer. Also a layerof silver is used, sandwiched between layers of nichrome. The term“nichrome” is used to designate a layer which includes some combinationof nickel and chromium, at least some of which is in its metallic state,although same may be oxidized. In a similar way, the term “silver” meansthat the layer consists essentially of metallic silver, but may includesome other elements in small concentrations that do not adversely affectthe performance characteristics of the silver in the system as a whole.Bent or toughened silver coated glass is taught in European PatentApplication 87300601.9 published as No. 0233 003. An additional layer ofaluminum, titanium, zinc, tantalum or zirconium is used over the silverlayer, or both over and under the silver layer. In recent years, thepopularity of coated glasses has occasioned numerous attempts to achievea coated glass article which, prior to heat-treatment, can be coated,and which thereafter, can be heat-treated without adversely changing thecharacteristics of the coating or the glass itself (i.e., the resultingglass article). One of the reasons for this is, for example, that it canbe extremely difficult to achieve a uniform coating on an already bentpiece of glass. It is well-known that if a flat glass surface can becoated and thereafter bent, much simpler techniques can be used to get auniform coating than if the glass has been previously bent. This is truefor architectural, automotive, and residential glasses.

Various difficulties have been encountered by those skilled in the artin developing commercially suitable coatings for architectural andautomotive glazing. In particular, it has proved difficult to achievecoatings which provide good attenuation of direct solar radiation, thatis, good anti-solar properties. There has long been need in the glazingindustry for coating systems which can be uniformly deposited,especially by sputtering onto large surface areas with fast depositionrates, low deposition power density, good film quality, including highfilm durability, bulk or near bulk density, and long shelf life. As usedhere, large area deposition refers to deposition onto transparentsubstrates suitable in size for architectural and automotive glazingapplications.

It is an object of the present invention to provide coated articlesmeeting some or all of these industry needs. In particular, it is anobject of at least certain preferred embodiments of the invention toprovide heat-treatable coated glass articles comprising a substantiallytransparent glass substrate with a substantially transparent coating onthe surface of the substrate, which coating has good transmittance ofvisible light as well as good anti-solar performance characteristics. Inaccordance with certain preferred embodiments, it is a further object toprovide glazing units incorporating such coated glass. It is an objectof at least certain preferred embodiments of the invention to provideheat-treatable coated glass articles comprising a substantiallytransparent glass substrate with a substantially transparent coating onthe surface of the substrate, which coating has medium level oftransmittance of visible light as well as extremely high anti-solarperformance characteristics. Such coated articles can be used forarchitectural purposes and automotive applications, e.g., windshieldswith heat shielding properties, or windshields with defrosting andanti-fogging properties.

It is a further object of the invention to provide methods ofmanufacturing the aforesaid coated articles. In accordance withpreferred embodiments, such manufacturing includes applying a coating inaccordance with the invention. Optionally, the methods disclosed herefurther include the steps of applying an electrically conductive busbar, if desired, and performing heat treatment of the coated article,e.g., bending or tempering, and also optionally conducting laminatingprocesses.

Additional objects and advantages of the present invention will bereadily understood by those skilled in the art given the benefit of thefollowing disclosure of the invention and detailed description ofpreferred embodiments.

SUMMARY

In accordance with a first aspect of the invention, a heat-treatable,coated glass article of manufacture comprises a substantiallytransparent substrate with a substantially transparent multi-layercoating on a surface of the glass substrate. The substantiallytransparent coating comprises a first anti-reflection layer ofdielectric material overlying the surface of the substrate. Preferably,the anti-reflection layer is directly on the surface of the substrate.As used here and in the appended claims, any particular layer of thesubstantially transparent, multi-layer coating is said to be “directly”on or to “directly” overlie the substrate or another layer of thecoating if no other layer of the coating is positioned between them. Inthis regard, any particular layer of the coating may be said to liedirectly on another layer of the coating notwithstanding that there maybe a slight transition zone between the two layers involving migrationof the material of one layer into the other and/or interlayer reactionproducts different from the primary composition of the layers. A firstbuffer layer, most preferably a chromium buffer layer, overlies thefirst anti-reflection layer. Preferably it lies directly on theanti-reflection layer. A chromium buffer layer, as that term is usedhere, means a layer which is essentially metallic chromium, such as alayer deposited by sputtering from a chromium metal target in an inertatmosphere. It may be in part oxidized, especially in preferredembodiments wherein the chromium buffer layer scavanges oxygen from anadjacent silver or copper metal or silver-copper mixed metal IRreflective layer and/or from anti-reflection layers during a heattreatment step, as further discussed below. An infrared reflective layerof silver metal or copper metal or silver-copper mixed metal directlyoverlies the first chromium buffer layer. A second chromium buffer layerdirectly overlies the infrared reflective layer. Finally, a secondanti-reflection layer of dielectric material overlies the second bufferlayer. Preferably, it directly overlies the second buffer layer.Preferably, the first and second anti-reflection layers of dielectricmaterial are SnO₂, in view of the good D.C. magnetron sputter depositionproperties of SnO₂ and its compatibility with other preferred materialsof the film stack coating disclosed here. Other suitable anti-reflectivematerials for use in the coating include other oxide and nitradematerials, such as, for example, WO₃, TiO₂, ZnO, BiOx and Si₃N₄.Additional suitable anti-reflection layer materials will be apparent tothose skilled in the art given the benefit of this disclosure.Similarly, the use of copper, copper-silver, or most preferably silverin the IR reflective layer, especially with the chromium buffer layerssandwiching it, provides highly durable coatings which areheat-treatable and, in fact, even yield improved spectral propertiesupon undergoing heat-treatment. That is, especially in preferredembodiments, heat treatment of the system with or without the IRreflective layers shows several significant effects. First, opticaltransmittance of the coated article improves upon heat treatment. Thereis a temperature threshold to start transparency improvement, around400° C., to start the oxidation of the buffer layers. Second, electricalresistance reduces upon heat treatment e.g., sheet resistance of 6 Ohmmay be reduced to 3 Ohm after heat treatment. This improvement in sheetresistance is believed due to the diminishing of interface scattering atthe abrupt Ag—Cr. The degree of interface by forming an extendedinterface of Ag—CrOx upon heat treatment. Crystalinity degree of the Agfilm may also improve upon heat treatment, producing increasedconductivity. This effect is achieved at least in preferred embodimentswithout noticeable degradation in the IR properties of the system. Thisexcellent electrical conductance of the system allows the electricalheating of the coated glass in certain preferred embodiments byconducting an electrical current through the Ag layer. Third, opticaltransmittance of the system with anti-reflecting oxide layers improves,as does durability as compared with buffer-silver-buffer three-layersystem.

Unless the individual instance of usage clearly indicates otherwise,reference herein to heat-treatable glass should be understood to meanglass with a coating according to the present invention, which has notbeen heat-treated (but which can undergo heat treatment successfully inaccordance with the principles disclosed here) or which has not beenheat-treated,. The term heat-treated is used to mean glass which hasbeen subjected to a heat-treating process, such as tempering, annealingand/or bending, etc.

It is one advantage of the present invention that the heat-treatable,coated glass articles disclosed here exhibit certain improvements orchanges in spectral properties upon undergoing heat-treating (e.g., attemperatures of about 600° C.). Visible light transmittance increasesand sheet resistance decreases, and both mechanical stability andenvironmental stability improve with heat-treating. In a typicalembodiment employing a multi-layer coating deposited by D.C. magnetronsputtering on clear soda-lime-silica glass having a glass thickness from2.2 mm thick for an automotive windshield application to 6 mm thick forcommon architectural applications, using SnO₂ layers about 20 nm to 60nm thick for the anti-reflection layers, chromium buffer layers about 1to 4 nm thick, and a silver metal IR reflectance layer 6 nm to 17 nmthick, emissivity may improve, typically, from a value of 0.15 to 0.01,visible transmittance may increase or may reduce, e.g., from a value ofabout 85% to about 70%, and sheet resistance will improve from about 13Ohm/sq. to only about 1.5 Ohm/sq., with no haze occurring. Thus, thecoated glass disclosed here can be used as different products. Beforeheat treatment, coated glass in accordance with an embodiment of theinvention may have grey-blue color and Tvis of 50% to 70%. Afterheat-treating, the same glass may have Tvis of about 70% to 85% and becolorless.

In accordance with certain preferred embodiments, such heat-treatable,coated glass is especially well-suited for use in motor vehiclewindshield applications with high transmittance, low visible lightreflectance and high energy reflectance, wherein a polyvinyl butyryl orother suitable polymer sheet is sandwiched between one coated glasssheet as disclosed here and an uncoated sheet. Certain especiallypreferred embodiments employing a coating having the above five layercoating structure, wherein the first buffer layer is a chromium bufferlayer of 2 nm and the second buffer is a chromium buffer layer of 2.5nm, and the infrared reflective layer is a silver metal layer 10 nmthick, when the glass of the windshield (in total for both glass sheets)is about 2.2 mm thick soda-lime-silica glass, have visible lighttransmittance greater than 76%, solar energy transmittance less than50%, and solar reflectance (IR region) of at least 25%. In suchespecially preferred windshield embodiments, and in other preferredembodiments of the invention disclosed here, the infrared reflectorlayer is silver and each of the chromium buffer layers has a thicknesswhich is about 10% to 30% of the thickness of the silver layer afterheat treatment. In such especially preferred windshield embodiments, andin other preferred embodiments of the invention disclosed here, thefirst buffer layer is about 20% thinner than the second buffer layer.

In accordance with certain preferred embodiments, such heat-treatable,bendable, coated glass is especially well-suited for use inarchitectural applications, especially for round buildings or buildingswith cylindrical outside elevators. Certain especially preferredembodiments employing a coating having the above five layer coatingstructure, wherein the buffer layers are chromium buffer layers of 4 nmfor first buffer and 4 nm for the second buffer the infrared reflectivelayer is silver metal 14 nm thick, and the glass of about 6 mm thicksoda-lime-silica glass, have the ratio of visible lighttransmittance/total solar energy transmittance of about 50/27. Thisassumes, for example, a 6 mm-12 mm-6 mm two pane configuration, with thecoating at the surface No. 2. Such terminology, when used herein, meansthat a first 6 mm pane in spaced 12 mm from the second 6 mm No. 1; itsinside surface is surface No. 2; etc.

In accordance with another aspect, a heat-treatable coated glass articleis provided, having a substantially transparent coating, preferablydeposited on soda-lime-silica glass by D.C. magnetron sputtering,wherein the coating comprises:

a first anti-reflection layer of dielectric material overlying the glasssubstrate

a first buffer layer overlying the first anti-reflection layer

a first infra-red reflective layer of silver metal directly overlyingthe first buffer layer

a second buffer layer directly overlying the infra-red reflective layer

a second anti-reflection layer of dielectric material overlying thesecond buffer layer

a third buffer layer overlying the second anti-reflection layer

a second infra-red reflective layer of silver metal directly overlyingthe third buffer layer

a fourth buffer layer directly overlying the second infra-red reflectivelayer

a top anti-reflection layer of dielectric material overlying the fourthbuffer layer.

In accordance with certain preferred embodiments, such heat-treatable,coated glass is especially well-suited for use in motor vehiclewindshield applications, wherein a polyvinyl butyral (PVB) or othersuitable polymer sheet is sandwiched between one coated glass sheet asdisclosed here and an uncoated sheet. Such preferred embodiments havevery low reflectance of visible light and high transmittance of visiblelight, as well as low total solar energy transmittance and high solarreflectance (IR region). Certain especially preferred embodimentsemploying a coating having the above nine layer film stack, wherein thebuffer layers are chromium buffer layers of 1 nm to 4 nm thickness, theinfrared reflective layer is silver metal around 50 nm to 60 nm thick,when the glass of the windshield (in total for both glass sheetslaminated with PVB) is about 5.5 mm thick soda-lime-silica glass, havevisible light transmittance greater than 75%; total solar energytransmittance less than 50%; and solar reflectance (IR region) of atleast 25%. In such especially preferred windshield embodiments, and inother preferred embodiments of the invention disclosed here, eachinfrared reflector layer is silver and each of the chromium bufferlayers has a thickness which is about 10% to 30%, the thickness of thesilver layer after heat treatment.

The chromium buffer layers are found to perform a crucial role inrendering the coated glass articles disclosed here durable andeffective. Without wishing to be bound by theory, it is currentlyunderstood that the chromium buffer layers, although deposited aschromium metal, oxidize to some degree, especially during heat-treatmentof the coated glass. The buffer layers oxidize by taking oxygen fromadjacent layers, such as SnO₂ or other oxide material of an adjacentanti-reflection layer. There is a resulting increase in volume of thechromium buffer layer and corresponding increase in buffer layer densitywithout cracking of the buffer layer. This is highly advantageous, sincethe buffer layer should be crack-free and void-free following heattreatment to prevent oxygen diffusion through the buffer layer to thesilver metal IR reflection layer. Also, the high-density of the bufferlayers reduces or eliminates the adverse affects of migration of silverinto the buffer layers. Thus, long term durability and performance areachieved in the multi-layer coated, heat-treatable glass articlesdisclosed here. In preferred motor vehicle windshield embodiments of thepresent invention, the multi-layer heat-treatable coating is provided onone of the two glass panes which sandwiched between them a PVB sheet.Preferably, the coating is provided on the inside glass pane (i.e., theone facing the exterior pane vehicle passenger compartment rather thanthe exterior pane), most preferably on the so-called surface No. 2 ofthe windshield, i.e., on the outside surface of the inside pane (i.e.,adjacent the PVB sheet). The two glass panes, one coated and oneuncoated, typically are paired and bent together. In accordance withpreferred embodiments, special powder to prevent the glass panessticking together are usually used between the matched panes during suchbending process can be eliminated. The multi-layer coating serves toprevent sticking. Moreover, the multi-layer coating in accordance withpreferred embodiments is sufficiently durable and though, that it can beplaced into contact with the second glass pane during the bendingprocess without causing unacceptable scratching or other degradation ofthe coating.

In accordance with another aspect of the invention, methods are providedfor making the coated article disclosed above. Such methods compriseproviding a substantially transparent substrate, typically withappropriate surface preparation steps being performed on the surface tobe coated. The multi-layer, anti-solar coating is then formed on thesurface of the substrate. The first anti-reflection layer of dielectricmaterial is deposited, followed by the first chromium buffer layer,followed by the silver metal infra-red reflective layer, followed by thesecond chromium buffer layer, followed by the second anti-reflectionlayer. In accordance with preferred embodiments, each of the layers ofthe substantially transparent coating is deposited by sputtering in aseries of sputter stations arranged sequentially in a single sputteringchamber through which the transparent substrate passes at constanttravel speed. Suitable partitions, such as curtains or the like,separate one sputter station from the next within the sputteringchamber, such that different deposition atmospheres can be employed atdifferent stations. A reactive atmosphere comprising nitrogen or oxygenor both can be used, for example, at a first station to deposit ananti-reflection layer, followed by a non-reactive atmosphere consistingessentially of argon or other suitable inert gas at a subsequent stationfor depositing the silver metal IR reflection layer.

In accordance with certain highly preferred embodiments of themanufacturing method disclosed here, the substantially transparentcoating is deposited by multiple passes, preferably two passes throughsuch multi-station sputtering chamber. If the multi-station sputteringchamber has a sufficient number of cathodes, e.g., at least nine cathodematerials mentioned above, this method is especially suitable, forexample, for depositing the nine layer coating disclosed above in asingle pass. Alternatively, during each of the passes through thesputtering chamber, a multi-layer coating is deposited comprising theaforesaid first anti-reflection layer, first chromium buffer layer,silver metal layer, second buffer layer and second anti-reflectionlayer. Coatings formed in accordance with such multi-pass methods of theinvention are found to have substantially improved coating properties,including especially colour spectral uniformity.

It will be apparent to those skilled in the art in view of the presentdisclosure, that the present invention is a significant technologicaladvance. Preferred embodiments of the substantially transparent coatingsdisclosed here have excellent spectral performance characteristics,including excellent transmittance of visible light and advantageouslyhigh anti-solar properties, that is, high attenuation levels of directsolar radiation. Employing the above disclosed silver metal infra-redreflective layer, sandwiched between chromium buffer layers, togetherwith the anti-reflection layers results in novel multi-layer coatingswhich are highly suitable for large area deposition by planar DCmagnetron sputtering. Fast deposition rates can be obtained, evenemploying advantageously low deposition power densities. The resultingcoating has high durability, bulk or near bulk density and long shelflife.

Additional features and advantages of the various embodiments of thepresent invention will be further understood in view of the followingdetailed description of certain preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various preferred embodiments of the coated article of manufacture andmethod of manufacture disclosed above are discussed below with referenceto the appended drawing in which:

FIG. 1 is a schematic cross-sectional view of a coated article ofmanufacture according to a first preferred embodiment;

FIG. 2 is a schematic cross-sectional view of a second preferredembodiment;

FIG. 3 is a schematic illustration of a motor vehicle windshield(partially broken away) in accordance with a preferred embodiment,having the coating of FIG. 2 on surface No. 2 of the glazing panes; and

FIGS. 4-7 are graphical representations of the spectral properties ofvarious preferred embodiments described in Examples 1-3, respectively;

It should be understood that the schematic illustrations in FIGS. 1-3are not necessarily to scale. In particular, the thickness of thevarious individual layers forming the substantially transparentmulti-function coating are increased relative the thickness of thesubstrate for the purpose of clarity and ease of illustration.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

The coatings disclosed here are thermostable in that, when subjected tothermal stress, they are resistant, against degradation, most notably intheir capacity to block or transmit light. In addition, the term“thermostable” refers to a coating or coated article of manufacturewhich substantially retains its characteristic mechanical properties,such as body integrity, surface continuity, tensile strength andadhesiveness (e.g., between coating and substrate). The term “thermalstress” is herein taken to mean the stresses encountered upon exposureto high temperatures used for heat treatment, e.g., for tempering orbending the glazing substrate. Typically, such temperatures are in therange of 590° C. to 650° C. The solar coatings of the invention arethermostable at the tempering temperature of the glazing substrateand/or at its bending temperature.

It will be apparent to those skilled in the art, given the abovedisclosure and the following detailed description, that the coatedarticles disclosed here, comprising a substantially transparent glasssubstrate carrying a substantially transparent coating have numerouscommercially significant applications. For ease of discussion, thefollowing detailed description of certain preferred embodiments willfocus primarily on articles suitable for automotive or architecturalglazing applications. It will be within the ability of those skilled inthe art, given the above disclosure and this detailed description, toemploy the invention in alternative applications.

Referring now to FIG. 1, a coated article 10 is seen to comprise asubstantially transparent substrate 12 having a main surface 14 carryingsubstantially transparent, multi-layer coating 16. In preferredembodiments, the substantially transparent substrate is a flat orcurvo-planer pane of glass or glass ceramic. It is highly preferred thatthe substantially transparent substrate be a panel of glass selectedfrom the group consisting of soda-lime-silica glass, borosilicate glass,aluminosilicate glass, vycor, fused silica and vitreous silica. It isparticularly preferred that the glass be soda-lime-silica glass. Coating16 provides thermal insulation or anti-solar performance characteristicsfor the coated article. Coating 16 includes a first anti-reflectionlayer 18 directly on the surface 14. Numerous suitable materials foranti-reflection layer 18 are disclosed above and will be apparent tothose skilled in the art given the benefit of this disclosure. Mostpreferably anti-reflection layer 18 is formed of SnO₂. It should beunderstood that all references here and in the appended claims to anoxide, unless otherwise clear the context of any particular instance ofits use, are intended to include variations in the degree of oxidation.Chromium buffer layer 19 lies directly on anti-reflection layer 18.Silver metal layer 20 lies directly on buffer layer 19. Second bufferlayer 22 directly overlies silver metal layer 20. The overlyinganti-reflection film 24 is exposed to the atmosphere. It will be withinthe ability of those skilled in the art, given the benefit of thisdisclosure, to determine suitable thickness for the individual layers ofcoating 16, given the benefit of the disclosure, including suitablethickness for silver metal layer 20 adapted to the intended applicationof the coated article. Silver metal layers of greater thickness willprovide enhanced infra-red reflectivity, while thinner silver metallayers will provide increased transmittance of light in the visiblewavelength range. In accordance with certain preferred embodiments, thesilver metal layer has a thickness between 6 nm and 18 mm, morepreferably between 8 nm and 12 nm for automotive applications andbetween 8 nm and 16 nm for architectural applications.

It will be within the ability of those skilled in the art, given thebenefit of this disclosure, to employ additional coatings or additionalcoating layers with the multi-layer, heat-treatable, thermal insulationcoatings disclosed here. For example, transparent oxide or nitriteover-layers may be used at the surface of the coating exposed to theatmosphere. Also, colour control layer(s) can be used, preferably at theinterface of the coating with the glass substrate or on a differentsurface of the glass substrate. One or more other additional coatingsmay be used, e.g., an all-dielectric anti-reflecting coating system on adifferent surface of the glass substrate, preferably on the number 4surface of a double pane (interior side). Such AR coating improves thevisible transmittance of the overall coated article. Also, adhesionenhancing layer(s) can be used, e.g., at the interface of the coatingwith the glass substrate or on a different surface of the glasssubstrate.

The adhesion increasing layer or colour forming layer preferably has athickness less than 50 Å and is formed preferably of silicon or tungstenmetal. It will be within the ability of those skilled in the art, giventhe benefit of this disclosure, to select a suitable material andthickness for the colour control layer to achieve both enhanceduniformity and desired hue or colour of the coated article. Referencehere to uniformity of colour refers to reduction in blotchiness or thelike which may otherwise appear in a coated article

An alternative preferred embodiment of the coated articles disclosedhere is illustrated in FIG. 2, having a substantially transparentsoda-lime-silica glass substrate 32. A substantially transparent,heat-treatable coating 36 is carried on surface 34 of substrate 32. Incoating 36, first anti-reflection layer 38 directly over the surface 34of substrate 32.

The anti-reflection layer 38 in coating 36 of coated article 30 iscomparable to anti-reflection layer 18 in the embodiment of FIG. 1.Directly overlying anti-reflection layer 38 is a first buffer layer 40,preferably a chromium buffer layer, for the reasons discussed above.Silver metal layer 42 in the embodiment of FIG. 2 corresponds generallyto silver metal layer 20 in the embodiment of FIG. 1. Similarly, secondbuffer layer 44 corresponds generally to buffer layer 22 in theembodiment of FIG. 1. It will be within the ability of those skilled inthe art to select a suitable thickness for buffer layer 40, inconjunction with selection of the thickness of buffer layer 44, toprovide good protection for the silver metal layer 42 and the otherlayers of coating 36 within the constraints of meeting spectralperformance requirements in the finished article. Oxide layer 46directly overlies record buffer layer 44, and may be deposited in twoparts. Specifically, if a double pass sputtering deposition is carriedout as disclosed above, a first portion of oxide layer 46 may bedeposited at the last deposition station during the first pass of theglass substrate through the sputtering chamber. The second portion wouldthen be deposited at the first deposition station during the final pass.Third buffer layer 48 directly overlies oxide layer 46. Second IRreflection layer 50 directly overlies third buffer layer 48. Fourthbuffer layer 52 directly overlies silver metal layer 50. Outeranti-reflective layer 54 directly overlies fourth buffer layer 52, andis exposed to the atmosphere or to the space between pane 32 and asecond, coated or uncoated pane used with pane 32 to form adouble-glazed unit. Such space between two panes can be a vacuum orfilled with inert gas. The coated surface also can be positioned to lieagainst a PVB laminating sheet in a windshield construction or the like.Anti-reflection film 54 in the embodiment of FIG. 2 correspondsgenerally to tin oxide or other oxide anti-reflection layer 24 in theembodiment of FIG. 1. The thickness of the outer anti-reflection layer,that is, anti-reflection layer 24 in FIG. 1 and 44 in FIG. 2, isselected to provide, in conjunction with the other layers of thecoating, suitably low reflectance of visible light, with reflectancecolor preferably being neutral or grey-blue in the unheat-treatedcondition.

In accordance with certain preferred embodiments, the coated article 30is subjected to a tempering step subsequent to deposition of the coating36. Coating 36 survives exposure to the high temperatures required fortempering a glass substrate, such as a soda-lime-silica glass substrateintended for architectural or automotive applications.

FIG. 3 illustrates a motor vehicle windshield partially broken away, inaccordance with a preferred embodiment. A first pane 62 is laminated toa record sheet 64 by PVC sheet 66 between them. The inside pane 62,i.e., the one toward the motor vehicle passenger compartment, was bentin tandem with outer pane 64 and then separated for laminating. Aheat-treatable, multi-layer coating 70, in accordance with the presentdisclosure is on surface No. 2 of the windshield, i.e., inside surface68 of outside pane 64. Preferably coating 70 is in accordance with thecoating shown in FIG. 1 or FIG. 2. Above figure showing two panes ofglass window, withe the temperable multi functioning coating on the No.2 surface is necessary here.

The heating temperature/time profile of the bending furnace or lehr usedfor bending a heat-treatable coated glazing of the present invention isimportant. Suitable lehrs include, for example, a Tamglass bendingfurnace for simultaneous shaping of the two panes of an automobilewindshield by gravity sag forming. The top pane preferably is coatingfree and the inside of the lower pane comprises the coating. Suchbending furnace has five thermal zones. A first heating zone is fromroom temperature to 350° C. A second heating zone is from 350° C. to620° C. A third heating zone is the bending zone and the last two zonesare the cooling regions where glass cool downs slowly at first and thenfaster. The total time of the bending process is typically about 30minutes: 15 min. for heating & bending and 15 min. for cooling. The bestresults of bending in the third zone occur for typical automotivesoda-lime-silica glass, at about 615° C. over 45 to 60 seconds. It willbe within the ability of those scheduled in the art to determinealternative suitable temperature/time profiles given the benefit of thepresent disclosure.

Preferred embodiments of the coated articles disclosed here can beprepared in accordance with various suitable techniques employingcommercially available equipment and materials. Preferably, thesubstantially transparent dual-function coating is formed on the surfaceof the substantially transparent substrate by cathodic sputtering. Inaccordance with certain preferred embodiments, a coated article ismanufactured by depositing each of the layers of the coating insequence. Preferably, each of the layers is deposited in turn as thesubstrate travels continuously through a multi-station sputteringchamber. Thus, in manufacturing the embodiment of FIG. 1, for example,as the substrate passes through a first sputtering station within suchmulti-station chamber, the first anti-reflection layer of dielectricmaterial is deposited by DC magnetron sputtering onto the surface of thesubstrate. Depending on the substrate travel speed, depositionparameters, and the thickness of the anti-reflection layer, one, two ormore sputtering stations can be used to deposit the same coatingmaterial. In this way, one can achieve shorter deposition cycle time.After having deposited the first anti-reflection layer onto the glasssurface, the buffer layer and infrared reflective layer are thendeposited by sputtering as the substrate passes through a subsequentstation of the multi-station chamber. The second buffer layer isdeposited at a subsequent station within the chamber, and then thesecond anti-reflection layer is deposited on a subsequent station.Preferably, the substrate moves continuously through the chamber, suchthat the individual layers are deposited onto the substrate as it istraveling. The individual stations are sufficiently isolated by curtainsor other suitable partition means, such that the reactive atmosphereemployed at a first sputtering station does not contaminate thenon-reactive atmosphere employed at an adjacent station. In this regard,where less than all stations of a multi-station deposition chamber areto be employed, for example, where an eight-station chamber is to beused to deposit a four-layer coating, a station can be left unusedbetween one employing a reactive atmosphere and another employing anon-reactive atmosphere to achieve better isolation. Suitablemulti-station sputter deposition chambers are commercially available,including pilot plant size coaters, for example, Model Z600 from BalzersProcess System GmbH, D-63755, Alzenau, Germany, and full commercialscale coaters, for example, Interpane 1993 model Coater available fromInterpane Glass Industrie AG, Sohnr Eystasse 2137697 Lauenförde,Germany. Table A gives the typical process parameters for Model Z600pilot plant coater and for an Interpane 1993 Model production coater.

Parameters Z600 Interpane Maximum Substrate 40 × 50 600 × 300Dimensions, cm Background Pressure, 5 5 mbar (10⁻⁵) Power Density(Watt/cm²) 0.2-5   0.2-5   Working Pressure, 1.5-4   2-7 mbar (10⁻³)Argon, sccm sputter sputter Oxygen, sccm reactive reactive Nitrogen,sccm reactive reactive

Advantageously, such preferred multi-station sputtering chambers employsputter targets which are wider than the glass substrates being coatedand are mounted in a direction extending perpendicular to the traveldirection of the substrate. It will be within the ability of thoseskilled in the art to select suitable deposition conditions andparameters for magnetron DC sputtering of the various layers disclosedabove for the transparent coated articles of the present invention. Thefollowing deposition parameters are suitable for a typical depositionprocess to produce a heat-treatable, multi-layer coating in accordancewith the embodiment of FIG. 1 coating on a soda-lime-silica glasssubstrate 40 cm wide by 50 cm long traveling at a rate of 2 meters perminute through the sputtering chamber.

1. The sputtering chamber is initially evacuated to about 5×10⁻⁵millibar and then raised to an operating pressure of approximately3×10⁻³ millibar by the injection of operating gases at the varioussputtering stations.

2. Tin oxide anti-reflection layers are deposited by sputtering from apure tin target in an operating atmosphere of 3.2×10⁻³ millibar with anArgon/Oxygen flow rate ratio of 45/82, at a power level of about 4 to5.5 Watts/cm². The throw distance from the tin target to the substrateis typically about 5 to 15 cm.

3. The silver infra-red reflective layer is deposited from a pure silvertarget in a non-reactive atmosphere, for example, a substantially pureargon atmosphere, in an operating atmosphere of 2.0×10⁻³ millibar at apower level of about 0.4 to 2.6 Watts/cm². The throw distance from thesilver target to the substrate is typically about 5 to 15 cm.

4. The chromium buffer layers are deposited from a chromium target in anon-reactive atmosphere, for example, a substantially pure argonatmosphere, in an operating atmosphere of 11×10⁻⁴ millibar at a powerlevel of about 0.4 to 1.0 Watts/cm². The throw distance from the silicontarget to the substrate is typically about 5 to 15 cm.

In accordance with certain preferred embodiments, a substantiallytransparent, heat treatable coating in accordance with the structure ofthe embodiment of FIG. 2 described above is formed by passing thesubstrate through the multi-station sputtering chamber a first time,followed by passing it through the sputtering chamber a second time.Preferably the deposition characteristics and process parameters aremaintained the same before the two passes, such that substantiallyidentical sets of layers are deposited during each pass. Optionally, aslightly thicker final oxide layer is deposited for enhanced performancecharacteristics. In general, it would be understood that the thicknessof the deposited layers will be determined largely by the depositionpower level, working gas conditions, and the exposure time. The exposuretime is determined primarily by the speed at which the substrate istraveling through the sputtering chamber, although additional thicknesscan be achieved by employing multiple targets for a deposited layer.Throw distance is also a significant factor in determining layerthickness. In preferred embodiments employing sputtering targets widerthan the substrate, advantageously small throw distances can be usedwithout sacrificing uniformity of deposition thickness.

It has been found that, generally, multi-pane glazing systems employingthe heat-treatable coating of the present invention provide best resultswhen the coating is placed at the second surface as illustrated in FIG.3.

The present invention is further disclosed by the following examples,which are intended for purposes of illustration and not limitation.

EXAMPLES

The following examples illustrate coated articles according to theinvention, and their manufacture. In each of the following examples, asoda-lime-silica glass panel 30 cm wide by 30 cm long by 6 mm thick ispassed through a multi-station sputtering chamber, Model Z600 availablefrom Balzers Process System. At the same time, for visual inspection,measurement and characterizations, test pieces also were coated in thesystem. That is, same, a 5 cm wide by 5 cm long by 2.2 mm thick glasswas used for windshield applications and the same size test pieces of 6mm thick samples for architectural applications. The glass paneltraveled in each case through the sputtering chamber at a travel speedof 2 meters per minute. Immediately prior to entering the sputteringchamber, the glass panel surface to be coated was washed withdemineralized water (max 5 microsiemens) and substantially dried bypressurized air. For each of the examples, the sputtering conditions areprovided for each layer of the dual-function coating. In those of theexamples involving a double-layer structure, as disclosed above, thedeposition conditions and parameters were identical for the first andsecond passes unless otherwise stated.

The spectral properties were measured for the resultant coated articleof each example. Perkin Elmer Model Lambda 900 UV Vis NIRspectrophotometer was used to measure the optical performance of eachsample, e.g., transmittance, T %, reflectance from film side, R %, andreflectance from glass side, R′%, with all spectra being measured overthe 350 nm-2100 nm spectral region. Reference herein to spectralproperties in the IR range mean 750 nm to 2100 nm. The weighted spectralaverages of the visible region, T_(vis), R_(vis), R′_(vis) and otherperformance and color information shown in Tables 1-6 were determined bythe “Window 4.0”, and Uwinter and Usummer were calculated using the“Window 4.1” calculation program both publicly available from the USADepartment of Energy. These “U” values are a measure of overallconductance of the thermal energy in terms of Watt/m² K, calculatedusing the following table:

Outside Inside Wind Direct Temp Temp Speed Wind Solar T_(sky) Name (°C.) (° C.) (m/s) Direction (W/m²) (° C.) E_(sky) Uwinter Uvalue −17.821.1 6.7 0 Windward 0.0 −17.8 1.00 Solar −17.8 21.1 6.7 0 Windward 0.0−17.8 1.00 Usummer Uvalue 31.7 23.9 3.4 0 Windward 783.0 31.7 1.00 Solar31.7 23.9 3.4 0 Windward 783.0 31.7 1.00

In addition, the R_(s) surface resistance was measured by a Signatronfour probe, and emissivity, e was measured by an IR spectrometer andcalculated from the following equation:

e=1−(1/((1+0.0053)×R_(s)))²

Ref.: K. L. Chopra, S. Major, D. K. Pandya. It was found that measuredand calculated values fit well with each other for the films havingsurface resistance R_(s) less than 10 Omhs. The shading coefficient, sc,was calculated as the performance ratio, T_(vis)/T_(solar), was used todetermine the quality of the coatings. The theoretical limit of theT_(vis)/T_(total) solar ratio is 2.15.

EXAMPLE 1

This example shows the properties of a bendable and otherwise heattreatable coated glass suitable for motor vehicle windshieldapplications. In Table 1 below, the coated glass of this example isidentified by reference No. 1345. The same glass following heattreatment as described below is identified in Table 1 as Sample No.t1345. The same sample following such heat treatment and then laminationto an uncoated but otherwise substantially identical glass pane by meansof a PVB polymer layer sandwiched between the two glass panes isidentified by reference number L1345. The sample of this example is asingle silver/single pass sample. That is, the glass is passed throughthe DC magnetron sputtering chamber only once (hence, being referred toas a single pass coating) wherein it is coated, in order, with ananti-reflection layer, chromium buffer layer, silver layer, secondchromium buffer layer and finally second anti-reflection layer. Thus,the coated glass sample of this example has only a single layer ofsilver in the film stack which makes up the coating deposited on theglass in the sputtering chamber.

The glass panel was prepared and passed through the multi-stationsputtering chamber as described above. In this example, theheat-treatable multi-layer coating was SnO₂/Cr/A_(g)/Cr/SnO₂ where thefirst SnO₂ layer (directly on the glass substrate surface) and thetopmost SnO₂ layer have the same thickness, but the first Cr layer isthinner than the second Cr film. The total thickness of the coating wasaround 920 Å.

At station 1 within the multi-station sputtering chamber, a 39 nm thicklayer of SnO₂ was deposited by sputtering from a tin target at 5.1Watts/cm² in an atmosphere of Argon and Oxygen gasses with the flowratio of 45 to 82 sccm (i.e., with Argon and Oxygen flow rates of 45sccm and 82 sccm, respectively) at a vacuum level of 3.2×10⁻³ mbar.

At station 2, within the multi-station sputtering chamber, a 2 nm thicklayer of Cr was deposited by sputtering from a chromium target at 0.4Watts/cm² in an atmosphere of Argon gas with a flow rate of 20 sccm at avacuum level of 11×10⁻⁴ mbar. At station 3, within the multi-stationsputtering chamber, a 95 nm thick layer of Ag was deposited bysputtering from a Silver (Ag) target at 1.3 Watts/cm² in an atmosphereof Argon gas with a flow rate of 50 sccm at a vacuum level of 2.0×10⁻³mbar.

At station 4, within the multi-station sputtering chamber, a 2.5 nmthick layer of Cr was deposited by sputtering from a chromium target at0.4 Watts/cm² in an atmosphere of Argon gas with the flow rate of 30sccm at a vacuum level of 11×10⁻⁴ mbar.

At station 5, within the multi-station sputtering chamber, a 39 nm thicklayer of SnO₂ was deposited by sputtering from a tin target at 5.1Watts/cm² in an atmosphere of Argon and Oxygen gasses with a flow rateof 45 to 82 sccm at a vacuum level of 3.2×10⁻³ mbar.

The resultant coated glass panel, Sample No. 1345, had good coloruniformity. Its spectral properties are shown in Table 1 below, andspectral transmittance and reflection properties of the coated panel ofthis Example 1 are shown in the graphs of FIG. 4, wherein the horizontalaxis shows wavelength and the vertical axis shows level oftransmittance. Specifically, FIG. 4a shows intensity as a function ofwavelength for Sample No. 1345, that is, the coating as deposited. FIG.4b shows corresponding spectral properties for Sample No. t1345, thatis, the coating after heat treatment at 635° C. for 1 minute. FIG. 4cshows the spectral properties for Sample No. L1345, that is, thelaminated glazing system incorporating the glazing pane carrying theheat-treated coating and laminated by means of a PVB lamination layer toa second, uncoated glazing pane. In all cases, the spectral propertiesinclude transmittance (T %), reflection measured from the coated side (R%), and reflection measured from the uncoated side (R′%). As notedabove, coated articles of these examples were characterized byspectrophotometric measurements (Perkin Elmer Lambda 900 UV/VIS/NIRSpectrometer), resistance measurements (signatone four probes Model SYS301 instrument combined with Keithly Model 224 current source and Model2000 multimeter), and thickness measurements (Tencor Alpha Step Model500). Film thicknesses were measured by a Tencor Model Alpha step 500thickness measuring apparatus. Mechanical properties of the samples weredetermined by a Taber Abraser machine. Environmental stability of thesamples were evaluated by using a weathering cabin controlling ambienttemperature and humidity. Spectrophotometric measurements were takenover 300 nm to 2100 nm spectral region, including transmittance T %,reflection R % measured from the coated side, and reflection R′%measured from the glass (uncoated) side. As can be seen from Table 1 andthe graphs of FIG. 4, the coated panel prepared in accordance with thisExample 1 has excellent transmittance of visible light together withgood anti-solar properties. In addition, it has excellent environmentalproperties and long shelf life, specifically, passing a test of at leasttwo weeks in the humidity chamber at 60° C. and 95% relative humiditywith substantially no degradation observed throughout the sample surfaceof 40 cm by 50 cm, including the edges of the laminated product SampleNo. 1345. Furthermore, the coating process can be seen from thedescription here to be fast and economical, so as to be commerciallysuitable for producing automotive and architectural glazing products. Inthat regard, the sputter deposition process required only approximately2.5 minutes.

EXAMPLE 2

This example illustrates a double pass/double silver layer coatingsystem. That is, in this example, the soda-lime silica glass pane ispassed through the DC magnetron sputtering chamber substantially as inExample 1 above, but is then passed through the DC magnetron sputteringchamber a second time to produce a double-layer coating. The resultantcoating system deposited onto the glass surface has two IR reflectivelayers, that is, two layers of silver in the film stack which forms thecoating. It will be appreciated from the foregoing disclosure anddiscussion of the invention, that single pass, single silver layersystems are advantageous in that they are simpler to produce, and aresuitable for both automotive and architectural applications. Doublepass, double silver layer coating systems, however, in accordance withthe invention, also provide excellent spectral properties, environmentaldurability, etc. In accordance with this Example 2, the glass panel wasprepared and passed through the multi-station sputtering chamber asdescribed above in Example 1, except coating was doubled, that is, acoating system of SnO2/Cr/A_(g)/Cr/SnO₂/Cr/Ag/Cr/SnO₂ system wasdeposited with the respective thicknesses (measured in nanometers) of40/2/7/2/80/2/7/2/40. The total thickness of the resultant coating wasaround 182 nm. As mentioned above, in this example the coating wasproduced by passing the glass panel twice through the coater. The samedeposition parameters were maintained during the second pass. The coatedsample of this Example 2 was subjected to heat treatment as inExample 1. The resulting heat treated sample is identified in table 1below by reference No. t1288. The corresponding sample after beinglaminated to an uncoated but otherwise substantially identical pane bymeans of a PVB laminating layer is identified in Table 1 below byReference No. L1288. The spectral properties of Sample No. t1288 andSample No. L1288 are shown in Table 1 below. Spectral transmittance andreflectance properties of the coated panel of Example 2 are shown in thegraphs of FIG. 5a and 5 b. Specifically, FIG. 5a shows the spectralproperties T, R and R′ as intensity (%) as a function of wavelength forSample No. t1288. FIG. 5b shows the corresponding spectral propertiesfor the laminated Sample No. L1288. Performance values for Sample No.t1288 and Sample No. L1288 also are given in Table 1, below. The samplesof this Example 2 were found to have excellent environmental propertiesand a long shelf life comparable to those of Example 1. Morespecifically, as can be seen from Table 2 and the graph of FIG. 5, thecoated panel prepared in accordance with this Example 2 has excellenttransmittance of visible light together with good anti-solar properties.In addition, it has excellent mechanical properties, including longshelf life. Furthermore, the coating process can be seen from thedescription here to be fast and economical, so as to be commerciallysuitable for producing automotive and architectural glazing products.

EXAMPLE 3

Addition examples of the present invention were prepared to showarchitectural applications. Specifically, sheets or panes ofsoda-lime-silica glass having the same composition as in Examples 1 and2, being 6 mm thick, were used to prepare four architectural glassglazing products. In each case, a first 6 mm pane coated as describedbelow was spaced 12 mm from a second, uncoated 6 mm thick pane. Thecoating was carried on surface No. 2 of the resultant double panearchitectural glazing product. In all four samples, the coating systemwas deposited under the same conditions recited above in Example 1except as follows. In the first sample, Sample No. t1372 IG, thechromium and silver layers were thicker than in Example 1. Specifically,the silver layer was 14 nm thick and the two chromium layers, whichsandwich the silver layer between them, were each 4 nm thick. The tinoxide layers each was 22 nm thick. The spectral properties of theresulting Sample No. 1372 (tested as a single pane corresponding to thetest of Sample 1345 shown in FIG. 4a) carrying the coating systemSnO₂/Cr/Ag/Cr/SnO₂ are shown in FIG. 6a. Specifically, spectral valuesT, R and R′ are shown in FIG. 6a as a function of wavelength. In FIG. 6bthe corresponding spectral properties for the same sample after heattreatment are shown. The heat treatment was the same as that forExample 1. Additional performance characteristics of the heat treatedSample t1372 are shown in Table 1, below.

A series of additional samples in accordance with this Example 3 wereprepared, having the same chromium and silver film thicknesses as forthe first Sample No. 1372, above. Specifically, each of these additionalsamples was prepared in accordance with the method of Example 1, having4 nm thick (before heat treatment) chromium layers sandwiching betweenthem a 14 nm thick silver layer. The thickness of the tin oxide layersof these additional samples was varied. More specifically, the sampleswere prepared, each carrying a coating system of SnO₂/Cr/Ag/Cr/SnO₂ on 6mm thick glass, wherein each of the two tin oxide layers for the samplehad the thickness given below.

Sample No. Thickness of SnO₂ Layers t1372 22 nm t1376 35 nm t1378 55 nmt1377 65 nm

In each case, the thickness recited above is for each of the tin oxidelayers, rather than for the two tin oxide layers combined. FIG. 7 showsthe transmission spectra for these four samples. As seen there, as theoxide layer thicknesses increase, the transmission maxima or colorshifts from blue toward yellow. The same color shifts are observed forreflectance. Additional performance properties for these samples areprovided in Table 1, below. It should be noted that the transmissionspectra shown in FIG. 7 are for each of the samples following heattreatment as described for the sample of Claim 1, at 650° C. As notedabove, the performance characteristics provided in Table 1 below are foreach of the samples used in a “6+12+6” double glazing product, that is,a double glazing wherein a first 6 mm pane carrying the respectivecoating for that sample is paired with a second 6 mm, uncoated pane witha distance of 12 mm between the two panes. Excellent mechanicalproperties, including long shelf life are obtained for the heat treatedsamples and for the double pane glazing products made using the coatedsamples of this example.

TABLE 1 PERFORMANCE TABLE FOR MULTI-FUNCTIONAL GLAZING SYSTEM OpticalProperties Sol. Energy Solar Visible Region Region Shad- Fac- Relat.Reflection Reflection Therm. Prop. ing tor Heat Color Coordinates SystemTrans. Out In Trans. Out In Winter Summer Coef SHG- Gain TransmittanceReflectance (Out) Descr. Tvis R1 R4 Tsol R1 R4 U win U sum SCc Ce RHG TLa* b* RL a* b* AUTOMOTIVE GLAZING 1345 0.74 0.06 0.05 0.47 0.26 0.326.20 5.99 0.63 0.54 445 88.8 −3.20 0.38 29.3 7.34 −9.10 t1345 0.84 0.060.05 0.54 0.27 0.31 6.36 6.05 0.69 0.59 483 93.2 −2.20 2.64 29.6 5.23−9.30 L1345 0.76 0.12 0.12 0.48 0.29 0.26 6.24 5.98 0.63 0.54 444 90.1−3.70 1.96 40.5 5.94 5.89 t1288 0.76 0.07 0.07 0.50 0.27 0.30 6.36 6.100.65 0.56 458 89.8 −0.30 1.77 31.7 3.49 1.22 L1288 0.75 0.07 0.07 0.440.29 0.26 6.20 6.00 0.60 0.51 423 89.1 −2.00 3.73 32.7 0.75 −1.10ARCHITECTURAL GLAZING (6 + 12 + 6) 0.50 0.33 0.34 0.23 0.45 0.46 1.631.65 0.31 0.27 211 76.6 −12.00 −1.60 63.2 10.30 16.10 t1372 IG (6 + 12 +6) 0.37 0.47 0.48 0.20 0.49 0.50 1.63 1.65 0.28 0.24 188 68.6 −9.80−16.00 73.1 2.64 31.70 t1376 IG (6 + 12 + 6) 0.44 0.33 0.37 0.22 0.410.44 1.63 1.65 0.31 0.26 206 71.5 −4.60 14.90 64.1 1.35 −7.80 t1377 IG(6 + 12 + 6) 0.49 0.33 0.32 0.23 0.44 0.45 1.63 1.65 0.33 0.29 236 75.3−8.50 11.00 63.8 3.59 −1.00 t1378 IG

It will be apparent from the foregoing disclosure that alternativeembodiments are possible within the scope of the invention, including,for example, modifications to the preferred embodiments described above.It will be recognized by those skilled in the art, given the benefit ofthe present invention, that coated articles of manufacture in accordancewith the present invention can be prepared which are more or lesscolorless, depending on the thicknesses of the various films employed toform the coating. In particular, increasing the thickness of one or moreof the anti-reflection oxide layers and/or decreasing the thickness ofthe silver infra-red reflective layer can be employed to provide a morecolorless sample. This is consistent with the discussion in Example 7,above. Correspondingly, a more color-forming article can be prepared bydecreasing the thickness of the anti-reflection layers and increasingthe silver layer thickness. Additional alternative embodiments of thepresent invention, including those employing SnO₂ and the like can beemployed in accordance with the principles disclosed here to providecolor-forming or colorless coated articles within the scope of thepresent invention.

What is claimed is:
 1. A heat-treatable coated glass article comprisinga substantially transparent glass substrate with a substantiallytransparent coating on a surface of the glass substrate, thesubstantially transparent coating comprising: a first anti-reflectionlayer of dielectric material overlying the glass substrate, a firstchromium buffer layer overlying the first anti-reflection layer, aninfra-red reflective layer of metal selected from silver metal, coppermetal and a mixture of both, directly overlying the first buffer layer,a second chromium buffer layer directly overlying the infra-redreflective layer, and a second anti-reflection layer of dielectricmaterial overlying the second buffer layer.
 2. The coated article ofmanufacture according to claim 1 wherein the infra-red reflective layeris silver metal and the first and second anti-reflection layers each isSnO₂.
 3. The heat-treatable coated glass article according to claim 2wherein the thickness of each chromium buffer layer is 10% to 30% of thethickness of the infra-red reflective layer of silver metal.
 4. Theheat-treatable coated glass article according to claim 2 wherein thethickness of each chromium buffer layer is 1 nm to 5 nm and thethickness of the infra-red reflective layer of silver metal is 6 nm to13 nm.
 5. The heat-treatable coated glass article according to claim 4wherein the first and second anti-reflection layers of SnO₂ each has asubstantially uniform thickness from 20 nm to 50 nm.
 6. Theheat-treatable coated glass article according to claim 1 wherein saidglass is not heat-treated and, when the glass has a thickness of about2.2 mm to 6 mm, has the following characteristics: grey-blue color andsubstantially free of haze; visible transmittance of 40% to 70%; andsheet resistance of not more than 7 ohms/sq.
 7. The heat-treatablecoated glass article according to claim 1 wherein said glass isheat-treated clear glass and, when the glass has a thickness of about2.5 mm to 6 mm, has the following characteristics after heat-treatment:substantially free of haze; visible transmittance of 50% to 80%; andsheet resistance of not more than 5 ohms/sq.
 8. The heat-treatablecoated glass article according to claim 1 wherein the firstanti-reflection layer lies directly on the surface of the glass.
 9. Theheat-treatable coated glass article according to claim 8 wherein thefirst chromium buffer layer lies directly on the first anti-reflectionlayer.
 10. The heat-treatable coated glass article according to claim 9wherein the infra-red reflective layer directly overlies the firstchromium buffer layer.
 11. The heat-treatable coated glass articleaccording to claim 10 wherein the second chromium buffer layer directlyoverlies the infra-red reflective layer.
 12. The heat-treatable coatedglass article according to claim 11 wherein the second anti-reflectionlayer directly overlies the second buffer layer.
 13. The heat-treatablecoated glass article according to claim 1 wherein the substantiallytransparent glass substrate is soda-lime-silica glass.
 14. Aheat-treatable coated glass article comprising a substantiallytransparent glass substrate with a substantially transparent coating ona surface of the glass substrate, the substantially transparent coatingcomprising: a first anti-reflection layer of dielectric materialoverlying the glass substrate, a first buffer layer overlying the firstanti-reflection layer, a first infra-red reflective layer of silvermetal directly overlying the first buffer layer, a second buffer layerdirectly overlying the infra-red reflective layer, a secondanti-reflection layer of dielectric material overlying the second bufferlayer, a third buffer layer overlying the second anti-reflection layer,a second infra-red reflective layer of silver metal directly overlyingthe third buffer layer, a fourth buffer layer overlying the secondinfra-red reflective layer of silver metal, and a third anti-reflectionlayer of dielectric material overlying the fourth buffer layer.
 15. Theheat-treatable coated glass article of claim 14 wherein each of theanti-reflection layers is SnO₂ and the buffer layers each is a chromiumbuffer layer.